[Trilinos-Users] [EXTERNAL] NOX::Epetra::LinearSystemAztecOO

[Roger Pawlowski]

Hi Mike,

The "Required" interface is required to construct the 
NOX::Epetra::Group, not to construct the LinearSystem.  The linear 
system object is used to access the Jacobian operator and its inverse 
operator for solving Newton based systems.  The four constructors in the 
linear system object support different use cases.  Essentially, the 
fourth constructor you refer to allows for a user to supply their own 
Jacobian operator and their own preconditioner.  The other contstructors 
are for the use cases where some of this information is not present.  In 
that case, the required interface will provide a residual evaluation 
that can be used to construct the missing information.  If the Jacobian 
operator is not supplied it will used Jacobian-free Newton-Krylov 
methods to approximate the Jacobian vector products.  If a 
preconditioner is missing, there are multiple options including using 
the residual evaluation to brute-force a colored finite differnce 
Jacobian to get preconditioner entries to hand off to Ifpack or ML.

Roger


On 11/23/2011 09:49 PM, Mike Sussman wrote:
> Would someone please explain to me why the fourth constructor 
> in NOX::Epetra::LinearSystemAztecOO does NOT include the "required" 
> function evaluator computeF from NOX::Epetra::Interface::Required, but 
> only the Jacobian and preconditioner?  The words in the Detailed 
> Description seem to imply that the fourth constructor should include 
> NOX::Epetra::Interface::Required::computeF as a parameter.
>
> -- 
> Mike Sussman
>
>
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